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Monday, January 5, 2015

Five Good Reasons Why At Least 50% of Your 2015 'Cardio' Training Should Be High Intensity Interval Training (HIIT)

Remember: HIIT does not have to happen on the treadmill.

If you haven't already done so, I suppose you are currently revising last year's training regimen: Reviewing what worked and what didn't work; and thinking about (new) goals and the best ways to achieve them.

If you haven't yet decided on what type of cardio training you want to do, today's SuppVersity article may help you make the right endurance / cardiovascular exercise choices for 2015. In that, the headline already revealed: At least 50% of your 2015 "Cardio" training should be high intensity interval training (HIIT) - and here is why.

HIIT is more time efficient - Unless you have lost your hob and are looking to kill the newly won time in 2015, you are probably similarly short on time as most of us. Against that background, the mere time efficiency of HIIT workouts are an argument even the most feverish advocates of low-intensity hour-long cardio cannot deny (Gaesser. 2011; Gillen. 2013).

Figure 1: In contrast to often-heard claims, HIIT is not just a "glucose burner" it's also a fat burner. It does (a) increase the oxidation of fatty acids after the workout and (b) increases your muscles' and other cells' general ability to oxidize fat as fuel (see figure from Talanian. 2007).

"As few as 6 sessions of HIIT over a 2-week period for a total of about 15 minutes of very intense exercise (equating to approximately 600 kJ or 143 cal) have been shown to increase skeletal muscle oxidative capacity and alter metabolic control during aerobic-based exercise (Gibala. 2008). And 7 HIIT sesssions performed over 2 weeks significantly heightened whole body and skeletal muscle capacity for fatty acid oxidation during exercise in moderately active women (Talanian. 2007). For those who have limited time to work out, this makes HIIT an intriguing option" (Schoenfeld. 2009).

And even if your goal is not to get fitter, but rather to burn more energy, HIIT can do what steady state cardio will never achieve, i.e. burn 14.5 kcal/min (see "Tabata Workouts: Do They Work & How Energy-Demanding Are They? 14.5 Kcal/Min Sounds Nice, But You Must Earn It!" | learn more). In the end, short workouts will thus increase your 24h energy expenditure to the same extend endless steady-state workouts would do (Skelly. 2014).

"HIIT may help insufficiently active individuals overcome a major barrier to maintaining a physically active lifestyle, that of a perceived lack of time. An added bonus is that from a time:benefit perspective, HIIT may prove to be a good example where less can be more" (Gaesser. 2011).

And it does not even take a Tabata workout to time-efficiently improve your health. As a SuppVersity reader you will be aware that "4x4 Minutes of HIIT Per Week That's All It Takes For Already Well-Conditioned Individuals to Stimulate Mitochondrial Growth ➯ 15% Increase in VO2Max, Peak & Mean Power" | learn more.

HIIT has more favorable effects on your glucose metabolism and heart health - You probably have heard that 1h on the treadmill was the ideal exercise for the obese type II diabetic, right? Well, this may in fact be true, but the reason that's ideal for an obese type II diabetic is that even walking on a treadmill is a high intensity exercise for someone who weighs 300-450lbs.

Figure 2: A 2008 study in healthy, normal-weight young women proves: HIIT "cardio" training leads to significantly more pronounced improvements in all three central variables of glucose metabolism than a comparable steady-state "cardio" workout (Trapp. 2008).

That being said, for all of you with at least a decent amount of fitness, HIIT training with its ability to burn tons of glycogen within just a few minutes should be the preferred mode of exercise. A mode of exercise which has far more potent effects on the expression of the anti-diabetic, anti-obesity and anti-metabolic syndrome proteins AMPK and SIRT-1 than any other form of exercise (Gurd. 2010) and has thus not surprisingly been shown to have superior effects on central markers of glucose metabolism in a 2008 study by Trapp et al. - and that in healthy, lean, young women (see Figure 2).

A similar superiority has been observed by Weston et al. (2013) in patients with lifestyle-induced cardiometabolic disease. Their systematic review and meta-analysis in the British Journal of Sports Medicine indicates that "HIIT significantly increases CRF [cardio-respiratory fitness] by almost double that of MICT in patients with lifestyle-induced chronic diseases." (Weston. 2013).

HIIT exercise will help curb your cravings - While steady-state "cardio" has repeatedly been associated with increases in appetite, hunger and most importantly food intake, there is good evidence that "Intensity [is] the Key to Minimize Exercise Induced Cravings?" (learn more)

I don't want to repeat myself on this one. Instead I will just refer you to a recent SuppVersity article on that matter and the plethora of evidence that confirms the negligible or beneficial effects of high intensity interval training on appetite, hunger and how much food you eat and thus ruin any exercise-induced reduction in your daily energy balance (Alkahtani. 2014; Martins. 2014).

Before I go on to the #4 on the benefits list, I would yet like to
highlight the following result from a recent study from the University
college of London:

"Exercise increases neural responses in reward-related regions of the brain in response to images of low-calorie foods and suppresses activation during the viewing of high-calorie foods" (Crabtree. 2014)

Can't believe what you just read? Look at the figure on the right which
depicts the VAS scores for hunger, desire to eat, fullness, and thirst, during REST (black line) and EX (gray line) in N=15 lean healthy men who completed two
60-min trials—exercise and a resting control trial (REST).

Thus, the study clearly confirms the validity of the suggestion to stay scrap your steady-state cardio workouts and replace them with HIIT, in order to finally be able to stick to your diet plans and see the fat loss you are looking for.

HIIT ramps up the metabolism instead of ruining it - As long as you don't overdo it by training too often or extending your HIIT sessions to 1h, HIIT will produce a profound "after burn" that's 3x higher than in the case of classic steady-state "cardio" workouts.

Figure 5: EPOC
and corresponding additional energy expenditure in the high intensity 3x
Wingate group (SPIE) and the 30min continuous exercise group (HIE)
during the 30 min right after the workout (Townsend. 2013)

As a standalone, this previously reported benefit is hardly worth the paper it is printed on. In conjunction with the previously mentioned benefits, however, it is an important benefit of HIIT that must not be underestimated.

HIIT is perfectly scalable - Unlike steady-state cardio, where you would have to endlessly increase your workout times, HIIT workouts are easily scalable. You can either...

increase the resistance on your training device or run / cycle on a more difficult track (intensity increase),

increase the speed at which you run, pedal or row (intensity increase), or

reduce the time of active rest between the intervals (intensity increase)

and thus have many more options to tweak the workouts to your individuals needs. For beginners this is not that important. An obese type II diabetic has plenty of room to increase the pace and / or duration of his / her steady-state "cardio" workouts. A trained athletes, on the other hand, will soon hit a wall, when he / she begins to cycle at 90% intensity for 2h everyday.

Bottom line: As you can see, there are plenty of good arguments in favor of HIIT training. Arguments that do yet not warrant replacing "classic" steady-state endurance training altogether. In fact, comparisons of high intensity interval and classic endurance training in trained athletes show that both are equally effective (Owens. 2013). If you are a triathlete or other endurance athlete, your interpretation of the science presented in the study at hand must still be different. For you (as an endurance athlete), replacing 50% your sport-specific training, which is steady-state training, with HIIT isn't advisable. Adding one or the other HIIT session from time to time, on the other hand, is.

HIIT "cardio", steady-state "cardio" and the sympathetic and parasymphatic nervous system | more

For the average gymrat, important arguments to keep the classic cardio exercises in their routine can be (a) personal preference (even the best workout is only beneficial if you actually do it) and (b) the recovery of the sympathetic nervous system. While low intensity steady state cardio - if it's done in reasonable amounts - may actually improve the recovery of the sympathetic nervous system the day after a strength training session. A HIIT workout will further tax it. If you belong to those who hit the weights 5x per week, it may thus be wiser to stick to steady state instead of HIIT exercise as your preferred weight training regimen to give your sympathetic nervous system time to recover during a low intensity steady-state workout | Comment on Facebook!

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